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ADVANCES in NATURAL and APPLIED SCIENCES
ISSN: 1995-0772 Published BYAENSI Publication EISSN: 1998-1090 http://www.aensiweb.com/ANAS
2017 March 11(3): pages 54-63 Open Access Journal
ToCite ThisArticle: Ass. Prof. Dr. Mohammed I. Mohsin, Ass. Prof. Dr. Zainab H. Naji, Ali A.A. Abaas., Optimum Advances in Natural and Applied .Overhead Wind Turbine for an Energy Recovery System –Configuration of Cooling Tower
63-54);Pages: 3(11. Sciences
Optimum Configuration of Cooling Tower – Overhead Wind Turbine for an Energy Recovery System
1Ass. Prof. Dr. Mohammed I. Mohsin, 2Ass. Prof. Dr. Zainab H. Naji, 3Ali A.A. Abaas
1,2University of Technology in Baghdad, Mechanical Engineering Department, 3graduate student
Received 18 January 2017; Accepted 22 February 2017; Available online 26 March 2017
Address For Correspondence: Maruthamuthu Ramasamy, Assistant professor, Department of Computer Science &Engineering, RVS College of Engineering, Dindigul-624005, Tamilnadu,India.
ABSTRACT In this paper, the utility of an energy recovery wind turbine system has been investigated. Two vertical axis wind turbines (VAWTs) assembled with an enclosure were positioned above a full-scale cooling tower to use the exhaust air for electricity generation. The enclosure comprised of diffuser plate which draw more air to accelerate the flow. In addition, the enclosure design with guide vanes mounted upstream of the wind turbine to guide the air before it interacts with the turbine blades. Laboratory tests had been carried out to investigate two important parameters, namely, the rotor weight and vertical position of the WT in order to determine the maximum possible recovered power from the system. The net output power of heavy WT rotor was increased by about 36.7% over the light WT rotor for the same angle of attack and guide vanes, while the recovered energy was increased by 17.7Wwhen the heavy WT rotor was closer to the cooling tower fan and this increase was reduced to 10.1W for light WT rotor. The recovery energy from this wind generation system may be utilized for commercial as well as domestic purposes.
KEYWORDS: wind turbine, rotor, cooling tower, energy recovery system.
INTRODUCTION
Cooling towers are heat reject equipment ultimate to transfer waste heat to the atmosphere; large office
buildings, hospitals and schools typically install one or more cooling towers for building air-conditioning
system. Generally, cooling tower relies on power-driven fans to draw or force the air through the tower. The
recovering of part of the energy from the cooling- tower exhaust air by mounting a suitable type of wind
turbine, may be implemented under the energy recovery systems categorization.
Tong, et al. [1,2] mounted a vertical axis wind turbine (VAWT) with an enclosure in cross-wind orientation
above a cooling tower exhaust fan to harness the wind energy for producing electricity. The effects of VAWT
on the cooling tower air intake speed and its performance was calculated. The effects of VAWT on the current
consumption of the power-driven fan were also investigated. The enclosure design added to guide the wind
before the wind-stream interacts with the wind turbine blades and create a venturi effect (to increase the wind
speed). A scaled model (5-bladed H-rotor with 0.3m rotor diameter) was conducted in laboratory test which
showed no measurable difference in the air intake speed (1.6~1.8 m/s) and current consumption of the power-
driven fan do not effect in wind turbine. Kim, et al [3] used a blower for generating wind energy by studying a
simple wind tunnel, which was equivalent to natural wind. To analyze the relationship between the mechanical
and electrical power, the mechanical and electrical power in a small-scaled wind turbine were empirically
63-54, Pages: 7201 March) 3(11. Advances in Natural and Applied Sciences/7201 .,et al Ass. Prof. Dr. Mohammed I. Mohsin 55
measured. The data analyzed using the empirically obtained mechanical and electrical power will contribute to
obtaining the specification of a wind turbine generator, which produces the maximum power.
Mohammed [4] made a comparison between two and three blades Savonius wind turbine. Two models of
two and three blades were designed and fabricated from Aluminum sheet, each of them had an aspect ratio of
(H/D =1), the dimension was ( H = 200 mm height and diameter D = 200 mm) and the blades were made of
semi – cylindrical half of diameter (d = 100 mm). These two models were tested and investigated by using a
subsonic wind tunnel. It was observed from the measured and calculated results that the two blades savonius
wind turbine was more efficient, it had higher power coefficient under the same test condition than that of three
blades savonius wind turbine. The reason was that increasing the number of blades led to increase the drag
surfaces against the wind air flow and caused to increase the reverse torque and leads to decrease the net torque
working on the blades of savonius wind turbine. Qasim. et all [5] designed the rotor wind turbine, which used
more effectively for the wind energy and depended on the acting area of the vanes. The frame design consisted
of three movable vanes to reduce the negative torque of the frame that rotates contrary to the wind. The wind
tunnel was used to measure the power coefficient, torque coefficient and angular velocity as a function of wind
velocity. The power coefficient was measured experimentally to be equals to 18% and 21% for three and four
frames, respectively. The rotor wind turbine was applicable internationally due to its high efficiency, simple
construction, and simple technology.
Akhgari [6] studied the performance of a vertical axis wind turbine with and without a diffuser. Direct
measurement force was applied to a scaled model of the rotor in a water tunnel. The experiment was conducted
at different tip-speed ratios. The turbine rotor with diffuser had maximum power coefficient of 0.35 and 0.26
without diffuser. When the diffuser was used in the configuration. The maximum power coefficient was
increased by 35%. The particle image velocimetry (PIV) technique was used to study the flow patterns
downstream of the turbine.
Each configuration (with and without a diffuser) considered six different tip-speed ratios. The flow physics
in each configuration was showed into the vorticity and the streamline plots.
Abdulrazek [7] constructed small wind turbine model with variable speed and pitch control in order to
investigate the effect of this control strategy on wind turbines by characterizing its design and output power.
Specifications and functions in addition to description of the Lab View program mentioned small wind turbine
model components. The output voltages and currents from the generator were measured at different wind
speeds.
B. Roscher [8] optimized the structural design of a VAWT rotor blade and to decrease the mass to area ratio
by varying blade shape and structural layout. The choice of mass to rotor area ratio as an optimization function
followed from the fact that this area was directly proportional to the energy output while mass drove production
and installation costs.
Hwang [9] described the performance improvement of the straight-bladed vertical axis wind turbine. To
improve the performance of the power generation system, which consisted of several blades rotating about axis
in parallel direction, the cycloidal blade system and the individual active blade control system were adopted,
respectively. Both methods were variable pitch system. For cycloidal wind turbine, aerodynamic analysis was
carried out by changing pitch angle and phase angle based on the cycloidal motion according to the change of
wind speed and wind direction, and control mechanism using the cycloidal blade system was realized for 1kw
class wind turbine. By this method, electrical power was generated about 30% higher than wind turbine using
fixed pitch angle method.
In the present research, a simple energy recovery system consisting of full scale cooling tower, vertical axis
wind turbine, and diffuser is designed, constructed and tested in order to determine the optimum configuration
of cooling tower-overhead wind turbine combination. The interest is focused on the effect of rotor weight and
turbine vertical position relative to cooling tower exhaust fan on the mechanical output power and recovered
power.
Test Procedure:
A special configuration has to be designed in order to harness the maximum amount of energy from the
cooling tower exhaust air. This configuration consist of a cooling tower which represent the unnatural wind
resource, and two vertical axis wind turbines installed in cross-air orientation at the exit of cooling tower, as
shown in Fig(1).
63-54, Pages: 7201 March) 3(11. Advances in Natural and Applied Sciences/7201 .,et al Ass. Prof. Dr. Mohammed I. Mohsin 56
Fig. 1a: Schematic of the two vertical axis wind turbines over the cooling tower fan
Test Rig Design:
A set of two vertical axis wind turbines (VAWT) was designed and fabricated at the power laboratory
(Mechanical Engineering Department – UOT), as shown in figure (1b).
Fig. 1b: cooling tower with vertical axis wind turbine system
Each turbine consists of 5-blades with H-rotor of 245mm diameter. The profile of each blade airfoil is
(MH114 13.02%) made from wood by CNC machine. The blade dimensions are 60mm cord, 9mm thickness
and a span of 350mm. The blades angle of attack can be adjusted to be 6 deg. or 12 deg. The turbines were
placed at a predefined position in cross-wind orientation facing the discharged wind from the cooling tower fan.
The VAWT were in a symmetrical order with the vertical distance between the discharge outlet ducts to the
center of the turbine at 260 mm as shown in Fig (2).
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Fig. 2: Schematic of wind turbine and diffuser
The horizontal distance between the center of the outlet duct to the center of turbine is set to be 230 mm. A
diffuser with four adjustable guide vanes was mounted upstream of the wind turbines as shown in Fig (2)
The optimum angle of the guide vans, б will be specified according to angle of attack, α as shown in the
velocity triangle, a represent the axial induction factor Fig (3). The angle of attack is calculated by: [1]
∝= tan−1 ((1−𝑎)𝑉 sin 𝜃
𝑈+(1−𝑎)𝑉 cos𝜃) (1)
With θ= б- ψ (2)
Ψ is the angle between U and horizontal axis which determined by blade position angle.
Fig. 3: Velocity triangle for the turbine blade and wind stream
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During the tests two geometrically similar sets of turbine rotors were used, they are only differ in their
masses. The heavy rotor set is named (rotor1), while the lighter rotor set is named (rotor2).
Turbines Position adjusting mechanism:
The vertical position of the wind turbine rotor relative to cooling tower exhaust fan plane can be adjusted
from the two rotor shaft bearings by means of sliding mechanism designed especially for this purpose.
Cooling tower:
An induced cooling tower (made by SINYU Company) was used in the present test as unnatural wind
resource for the wind turbine figure (4). The technical specifications of cooling tower are given in table (1).
Table 1: Cooling tower specifications
tower height (mm) 1120
tower outlet diameter (mm) 760
Air flow rate (m3/min) 85
Fan tip diameter (mm) 680
Circulating water flowrate (m3/h) 1.8-2.1
Fan rotational speed (RPM) 960
Rated fan motor power (w) 222.6
Fig. 4: Cooling tower
Measurement and Instrumentation:
The parameters have to be measured through experimental tests are; wind velocity, turbine rotation speed,
turbine output torque and cooling tower fan power consumption. To achieve these measurements, the following
instruments are required:
1. Anemometer
2. AVO meter
3. Tachometer
4. Torque meter
The anemometer (Type: VICTOR 816) was used to measure wind velocity at outlet cooling tower fan. The
power consumption of the fan motor of cooling tower was specified by measuring the current and voltage for
motor by AVO meter (type: VC3266L).
To measure the mechanical output power from wind turbine the speed of rotation and torque were measured
by tachometer type Lutron DT-2236 and pulley and rope torque meter.
Methodology:
The position of the wind turbines over the cooling tower fan (figure1) is mainly dependent on the wind
velocity profile at the fan outlet. An appropriate measurement method which was developed by Cooling Tower
Institute (CTI) [1] was adopted in the present work. Divide the duct area into a few concentric parts of equal
region. The outlet wind speed V was measured at 5 positions taken at each interval around the circle. The
average wind velocity at the outlet of the cooling tower was 5.3 m/s.
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Figure (7) shows the measured velocity profile of cooling tower exhaust air. Two peaks are appearing at the
left and right hands sides of the velocity profiles. These peaks are coincident within the two WT rotors.
Fig. 7: Velocity profile of cooling tower exhaust air
The WT output power and the net recovered power at given cooling tower fan speed are dependent on many
interconnected parameters, namely vertical distance between the cooling tower fan and WT, WT rotor design
mass, air angle of attack and guide angles. Eight cases were considered during the experimental tests to cover
all mentioned parameters. Table (2) shows these cases.
Table 2: Experimental test cases
Case Rotor No. Angle of attack (deg) Guide vane A (deg) Guide van B (deg)